Effect of serotonin on unidirectional ion fluxes in rat intestine in vivo

AIMS: A stimulating intestinal secretory effect is described in vitro and an inhibition with selective inhibitors of the different receptors of serotonin (5-HT), in vivo. But a direct effect, in vivo, in fully vascularized and innervated intestine has not yet been clearly evidenced. We studied the effect of 5-HT in anesthetized rats with ligated loops. This work, performed at 4 intestinal levels, allowed a comparison with the effects of a known stimulant of intestinal secretion, VIP, and a specific inhibitor of Na/H exchange, dimethylamiloride (DMA). RESULTS: 5-HT induced an inhibition of epithelial Na influx in agreement with the inhibition of Na/H exchanger, an inhibition of the influx of Cl, partially passive absorption following Na by paracellular route. A decrease of Na and Cl efflux was induced by 5-HT in duodenum, jejunum and ileum while in colon, a stimulation was obtained by intraluminal but not intravenous route. CONCLUSION: Even though 5-HT induced a liquid accumulation in all intestinal segments, the effect differed according to the intestinal level, either inhibition of absorption in the small intestine, or stimulation of secretion in the colon. The comparison of the effect of 5-HT with that of DMA shows that the inhibition of absorption is not only due to Na/H exchanger inhibition.     

The flow and fracture of unidirectional

A yielding criterion, based upon calculated internal stress distributions, was developed for composite materials under various externally applied biaxial tension loadings. The stress distributions were computed using the finite element technique; the criterion showed that the yield strength of the composite is significantly higher than the transverse uniaxial yield strength for a wide range of biaxial loadings. Limited amounts of preliminary data were generated (using the hydraulic bulge test to develop biaxial stress loadings) to validate the analytical yielding criterion. The data obtained showed better agreement with the new yielding criterion than they did with the existing Hill Criterion.     

The plastic anisotropy of an Al-Li-Cu-Zr alloy extrusion in unidirectional deformation

The plastic anisotropy resulting from the initial deformation microstructure and various aging treatments applied to several regions of an AA2090 near-net-shape extrusion has been investigated. Yield behavior was measured by uniaxial compression in multiple orientations of each region. Two models of the plastic anisotropy were generated: the Taylor/Bishop-Hill model, based on crystallographic texture, and the plastic inclusion model, developed by Hosford and Zeisloft,^[5] which incorporates anisotropic-precipitate effects. In overaged conditions, the Taylor/Bishop-Hill model adequately describes the observed plastic anisotropy. As the strengthening increment due to second-phase particles increases, there is a concurrent increase in the magnitude of the precipitate contribution to anisotropy. This anisotropy can not be accurately predicted solely by crystallographic texture. By incorporation of terms describing the precipitate anisotropy, the plastic inclusion model correctly predicts the yield strength variation in all regions tested. Examination of the fundamental interaction between matrix and precipitation strengthening reveals that there is a stronger basis for taking the critical resolved shear stress (CRSS) of the precipitates as a constant, rather than their effective yield strength. This consideration provides a more consistent and accurate form of the plastic inclusion model.     

The unidirectional solidification of Al-4 Wt pct Cu ingots in microgravity

Three Al-4 wt pct Cu alloy ingots, 10 mm in diameter and 25-mm long, were unidirectionally solidified in microgravity during the flight of a sounding rocket, with solidification rates of about 1.6 × 10⁻⁴ m/s and temperature gradients of about 2600 K/m. The apparatus was comprised of three muffle furnaces, which melted the ingots prior to the launch of the rocket. Unidirectional solidification of the ingots was accomplished by chill plates attached to the furnaces, which were withdrawn from the ingots during the microgravity portion of the flight, bringing the chill plates into contact with the bases of the capsules containing the ingots. Solidification was complete in less than 4 minutes. For comparison, several ground-based ingots were solidified in unit gravity under similar conditions. Metallographic analysis of the solidified ingots showed that the macrostructures of the unit-gravity and microgravity ingots were similar, all exhibiting columnar grains. However, the microstructures were significantly different, with the microgravity ingots exhibiting primary dendrite spacings about 40 pct larger than the unit-gravity ingots and secondary dendrite arm spacings about 85 pct larger. The larger dendrite spacings for the ingots solidified in microgravity are explained by lower dendrite growth velocities. The absence of convective mixing in the microgravity ingots slightly increased temperature gradients in the liquid portion of the alloy during solidification, which resulted in decreased growth velocities.     

The unidirectional solidification of Al-4 wt pct Cu ingots in microgravity

Three Al-4 wt pct Cu alloy ingots, 10 mm in diameter and 25-mm long, were unidirectionally solidified in microgravity during the flight of a sounding rocket, with solidification rates of about 1.6×10⁻⁴ m/s and temperature gradients of about 2600 K/m. The apparatus was comprised of three muffle furnaces, which melted the ingots prior to the launch of the rocket. Unidirectional solidification of the ingots was accomplished by chill plates attached to the furnaces, which were withdrawn from the ingots during the microgravity portion of the flight, bringing the chill plates into contact with the bases of the capsules containing the ingots. Solidification was complete in less than 4 minutes. For comparison, several ground-based ingots were solidified in unit gravity under similar conditions. Metallographic analysis of the solidified ingots showed that the macrostructures of the unit-gravity and microgravity ingots were similar, all exhibiting columnar grains. However, the microstructures were significantly different, with the microgravity ingots exhibiting primary dendrite spacings about 40 pct larger than the unit-gravity ingots and secondary dendrite arm spacings about 85 pct larger. The larger dendrite spacings for the ingots solidified in microgravity are explained by lower dendrite growth velocities. The absence of convective mixing in the microgravity ingots slightly increased temperature gradients in the liquid portion of the alloy during solidification, which resulted in decreased growth velocities. K.N. TANDON, formerly Associate Professor, Materials Engineering Laboratory, Department of Mechanical and Industrial Engineering, University of Manitoba     

Effects of nitro-L-arginine on blood pressure and cardiac index in anesthetized rats: a pharmacokinetic-pharmacodynamic analysis

PURPOSE: Nitric oxide synthase (NOS) inhibitors such as Nitro-L-arginine (L-NA) are being considered for the management of hypotension observed in septic shock. However, little information is available regarding the pharmacokinetic and pharmacodynamic properties of these agents. Our objective was to examine the relationships between L-NA plasma concentration and various hemodynamic effects such as cardiac index (CI), mean arterial pressure (MAP), and heart rate (HR) elicited by L-NA administration in rats. METHODS: L-NA was infused at doses between 2.5-20 mg/kg/hr in anesthetized rats over one hour. Hemodynamic effects and plasma L-NA levels were determined. RESULTS: Infusion of L-NA resulted in dose-dependent increases in MAP and systemic vascular resistance (SVR), decreases in CI, and minimal change in HR. The relationships between the hemodynamic effects and plasma L-NA levels were not monotonic, and hysteresis was observed. Using nonparametric analysis, the equilibration half-time (t1/2,keo) between plasma L-NA and the hypothetical effect site was determined to be 51.5 +/- 6.6 min, 42.4 +/- 10.1 min, 43.4 +/- 9.0 min for MAP, CI, and SVR, respectively (n = 14). The Emax and EC50 values obtained were + 32.5 +/- 8.4 and 2.6 +/- 1.3 microg/ml for MAP and -52.9 +/- 15.6 and 3.7 +/- 1.8 microg/ml for CI, respectively. CONCLUSIONS: Although L-NA can bring about beneficial elevation of MAP, such effect is always accompanied by a stronger effect on CI depression. Dose escalation of L-NA may bring about detrimental negative inotropic effect and loss of therapeutic efficacy.     

A new unidirectional solidification method to study gray cast iron

A new unidirectional solidification (US) method to study gray cast iron was developed. It is based on the combination of the classical Bridgman-type technique and the directional casting technique. By means of this method, it is possible to achieve, among others, the following aims:

The mode I fracture resistance of unidirectional fiber-reinforced aluminum matrix composites

The mode I fracture resistance has been measured for Al and Al/4 Mg matrix composites, unidirectionally reinforced with ceramic fibers, prepared using a squeeze casting technique. Effects of SiC particle additions have also been investigated. The Al/4 Mg system had a high toughness, whereas the Al matrix system had a relatively low fracture resistance. In all cases, the addition of particulates slightly decreased the resistance to crack growth. The fracture resistance was simulated by a ductile bridging model with plastic dissipation occurring within a zone governed by the fiber spacing. The tensile strength of these composites has been estimated, based on the resistance behavior and microstructure.     

The heat-transfer coefficient during the unidirectional solidification of an Al-Si alloy casting

The heat-transfer coefficient was measured during the unidirectional solidification of Al-7 wt pct Si alloy castings against a water-cooled Cu chill. Heat-transfer coefficients in the range of 2.5 to 9 kW m⁻² K⁻¹ were obtained with solidification vertically upward associated with higher values than solidification vertically downward. Horizontal solidification was associated with intermediate values. Profiles taken across the diameters of the casting surfaces at the interface with the chill showed them to be convex toward the chill by an amount which would produce a mean gap between the casting and the chill that would account for a significant proportion of the measured heat-transfer coefficient. The convex casting surfaces were attributed to the deformation of the initial casting skin by the thermal stress produced during solidification. Heat transfer during casting solidification is shown to be a complex mechanism controlled by the microscale surface roughness of the respective surfaces, mesoscale deformation of the casting skin by thermal stress, and macroscale movements of the casting and the chill due to their relative thermal expansion and contraction.     

The application of PEDRI to the study of free radicals in vivo

Proton-electron double-resonance imaging (PEDRI) has considerable value for study of the distribution and elimination pathways of nitroxide free radicals (NFRs). This has been illustrated by its use in studies of kidney function in the living rat in which the NFR proxyl carboxylic acid (PCA) has been employed as a 'tracer'. The technique, at its present stage of development, can demonstrate location of PCA in enough detail to observe the passage through kidney cortex and medulla differentially, and to see the NFR within the major abdominal blood vessels. These studies are helping towards an understanding of the metabolic fate of PCA, as well as providing information about kidney performance after challenge with a nephrotoxin. In addition, nitric oxide complexes, formed in vivo by providing rats with a nitrite-rich diet, have been observed ex vivo using PEDRI and field-cycled DNP.     

Prediction of creep-rupture life of unidirectional titanium matrix composites subjected to transverse loading

Titanium matrix composites (TMCs) incorporating unidirectional fiber reinforcement are considered as enabling materials technology for advanced engines which require high specific strength and elevated temperature capability. The resistance of unidirectional TMCs to deformation under longitudinally applied sustained loading at elevated temperatures has been well documented. Many investigators have shown that the primary weakness of the unidirectional TMC is its susceptibility to failure under very low transverse loads, especially under sustained loading. Hence, a reliable model is required to predict the creep-rupture life of TMCs subjected to different transverse stress levels over a wide range of temperatures. In this article, we propose a model to predict the creep-rupture life of unidirectional TMC subjected to transverse loading based on the creep-rupture life of unidirectional TMC subjected to transverse loading based on the creep-rupture behavior of the corresponding fiberless matrix. The model assumes that during transverse loading, the effective load-carrying matrix ligament along a row of fibers controls the creep-rupture strength and the fibers do not contribute to the creep resistance of the composite. The proposed model was verified using data obtained from different TMC fabricated using three matrix compositions, which exhibited distinctly different types of creep behavior. The results show that the creep-rupture life of the transverse TMC decreases linearly with increasing ratio of the fiber diameter to the ply thickness. The creeprupture life is also predicted to be independent of fiber spacing along the length of the specimen.     

The decline in serum albumin after conversion to high flux, high efficiency dialysis

In previous works using cytofluorometry, we demonstrated a broad range of IgE and IgE-receptor levels within individual mast cell populations with a 60 to 80% occupancy of the IgE receptors on mast cells by native IgE. This study was performed in order to confirm our previous findings using an independent method and to visualize the distribution of IgE-receptor complexes on mast cells at an ultrastructural level. For this purpose an indirect immunocolloidal gold-labelling technique has been applied. By counting the number of labelled gold particles, a relative measure of IgE-receptor surface expression and IgE occupancy of the receptors could be obtained. With respect to mast cell morphology and anti-IgE binding specificity criteria, 1% glutaraldehyde + 4% paraformaldehyde (1:1, vol/vol) was found to be the best of the seven fixatives applied in this study. This technique revealed numerous gold particles on the surface of mast cells from barrier-maintained rats (26 +/- 11 per mast cell section, mean +/- SD). Increased numbers of gold particles were counted if the mast cells were incubated with rat myeloma IgE (20 micrograms/ml) (46 +/- 33 per mast cell section, mean +/- SD). There were significantly increased numbers of gold particles on the mast cells of rats infected with N. brasiliensis (126 +/- 30 per mast cell section, mean +/- SD). This indicates that some of the IgE receptors (about 50% of the total number of IgE receptors in this case) on mast cells were occupied by native IgE and that parasite infection significantly increased the number of IgE molecules on the surface of the mast cells. These results correspond with the findings we have made using the cytofluorometric technique and confirm the large individual variations in the density of IgE receptors and IgE among the mast cells of a given cell population. Macrophages, lymphocytes and eosinophils, carrying the low-affinity IgE receptors (Fc epsilon RII), contained less than 5 (normal rats after incubation in rat IgE) or 10 (nematode-infected rats) gold particles per cell section. We also observed some non-granulated lymphocyte-like cells which bound a large number of gold particles after incubation with rat myeloma IgE (20 micrograms/ml), indicating that they contained IgE receptors Fc epsilon RI). They were interpreted as mast cell precursors which have previously been shown to exist in the peritoneal cavity.     

Diffusion in a unidirectional filament reinforced metal composite

A theoretical analysis has been developed to describe composition changes resulting from exposure of a unidirectional filament reinforced metal composite to an elevated temperature environment. The analysis was based on a simple superposition of finite-difference solutions of the diffusion equation, and was applicable to the case for which the filament and matrix metals comprised an isomorphous binary alloy system. The possibility of chemical reaction between filaments and matrix was excluded. Excellent agreement was obtained between calculated concentration profiles and results of quantitative electron microprobe analyses of nickel filament reinforced copper samples. However, the agreement was found to be quite sensitive to the dependence of diffusivity on concentration.     

Suppression of mouse skin papilloma by canthaxanthin and beta-carotene in vivo: possibility of the regression of tumorigenesis by carotenoids without conversion to retinoic acid

Inflammatory mediators such as interferon-gamma (IFN-gamma) are known to induce the expression of class II HLA (HLA-DR) and intercellular adhesion molecule 1 (ICAM-1) in a variety of cell types including epithelial cells. The coexpression of ICAM-1 and HLA-DR has been implicated in the pathogenesis of immune mediated ocular disease. We investigated the expression of ICAM-1 on the ocular surface of the rat eye following subconjunctival administration of IFN-gamma. A dose response study was performed using 100, 1,000 and 10,000 IU IFN-gamma/dose. The presence of ICAM-1 was determined using a standard immuno-peroxidase staining technique. The cornea, limbus, and conjunctiva were evaluated. The degree of reaction product in each area was graded by a masked observer. We found constitutive expression of ICAM-1 on the conjunctiva but not on the cornea. There was a significant relationship between the dose of IFN-gamma and the intensity of ICAM-1 staining on the conjunctiva (p < or = 0.05) and on the limbus (p < or = 0.04). Subconjunctival IFN-gamma had no effect on the expression of ICAM-1 in the cornea.